Nato defence ministers will consider the implications for Nato's own security of the "troubling escalation of Russian military activities" in Syria, secretary-general Jens Stoltenberg has said.

He said Nato is ready to deploy forces, if needed, to defend alliance member Turkey.

On Wednesday, Russian warships fired cruise missiles in the first combined air-and-ground assault with Syrian government troops since Moscow began its military campaign in the country last week.

Over the weekend, Turkey reported back-to-back violations of its airspace by Russian warplanes.

US defence secretary Ash Carter and his counterparts from the 27 other Nato nations had already been scheduled to meet today in Brussels.

Mr Stoltenberg told reporters the meeting will receive an update from its military commanders on the situation in Syria, as well as Afghanistan.

"In Syria, we have seen a troubling escalation of Russian military activities," Mr Stoltenberg said. "We will assess the latest developments and their implications for the security of the alliance. This is particularly relevant in view of the recent violations of Nato's airspace by Russian aircraft."

Nato on Monday issued a statement demanding that the violations cease. Russia called its penetration of Turkish airspace a minor incident that was unintentional. Mr Stoltenberg had already brushed off the Russian explanation.

"Nato is able and ready to defend all allies, including Turkey, against any threat," the secretary-general said. He said Nato had already increased "our capacity, our ability, our preparedness to deploy forces, including to the south, including in Turkey, if needed".

"We are constantly assessing the situation also with the Turkish government," Mr Stoltenberg said, adding that he would be meeting later with Turkish defense minister Mehmet Vecdi Gonul.

The defence ministers' meeting, their first since June, is also expected to approve ongoing efforts to re-equip Nato to meet a daunting array of contemporary security threats.

Decisions expected include approval for two new Nato headquarters units in Hungary and Slovakia to enhance their defences and speed the deployment of reinforcements sent by other alliance nations, and changes in the beefed-up Nato Response Force to, in Mr Stoltenberg's words, make it "bigger, faster and more capable".

"We are facing many challenges from many different directions," Mr Stoltenberg said. "Conflict, instability and insecurity."

"We will assess what we have to do to adapt Nato to current and future challenges," he said including cyberattacks and the mix of conventional and unconventional tactics commonly known as hybrid warfare.

Turkish president Recep Tayyip Erdogan warned Russia that its military action in Syria is endangering trade ties with Turkey.

Mr Erdogan said Ankara could look elsewhere for gas supplies and cancel the construction of its first nuclear power plant, which is being built by Russia. Russia supplies 60% of Turkey's gas needs.

Mr Erdogan, in comments published in the Hurriyet newspaper, accused Russia of attempting to increase its military presence and create a base in Syria and described the situation as "unacceptable".

In Russia, President Vladimir Putin's spokesman Dmitry Peskov said Mr Putin had been informed about Mr Erdogan's remarks but hoped they would not affect relations between the two countries.

"We sincerely hope that these relations will continue to expand according to the plans mapped out by Putin and Erdogan because this co-operation is genuinely mutually beneficial and is in the interests of both our countries," Mr Peskov told reporters.